VIEW ARTICLE

Ecology and Epidemiology

Analysis of Epidemics of Leptosphaerulina Leaf Spots on Alfalfa and White Clover in Time and Space. O. M. Olanya, Former graduate research assistant, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616, Current address: International Institute of Tropical Agriculture, Oyo Road, PMB 5320, Ibadan, Nigeria; C. Lee Campbell, Associate professor, Department of Plant Pathology, North Carolina State University, Raleigh 27695-7616. Phytopathology 80:1341-1347. Accepted for publication 25 July 1990. Copyright 1990 The American Phytopathological Society. DOI: 10.1094/Phyto-80-1341.

The spatial and temporal development of leaf spots on alfalfa (Medicago sativa ?Arc?) and Ladino-type white clover (Trifolium repens ?Regal?) caused by Leptosphaerulina trifolii were monitored during spring 1987, fall 1987, and spring 1988. In spring 1987, disease gradients developed from diseased alfalfa to both alfalfa and white clover; little disease developed on either host in plots with diseased clover at the focus. In fall 1987 and spring 1988, disease developed from alfalfa or clover on both hosts. Generally, disease increased more rapidly when alfalfa was the recipient host than when clover was, regardless of the host at the disease focus. Area under the disease progress curve (temporal) and volume under the disease progress curve (temporal and spatial) were greater when alfalfa was the recipient host than when clover was the recipient host. A theoretical model of disease progress in space and time based on the exponential model for distance and the monomolecular model for time adequately described several of the epidemics of Leptosphaerulina leaf spots. A new model based on the monomolecular model for time and a negative logistic model for distance better described the spatiotemporal progress of the epidemics during all three experiments. The cross-infectivity of isolates of L. trifolii on alfalfa and white clover was confirmed and, in this pathosystem, the recipient host plants of the disease gradient was more important in determining the characteristics of disease development than the host at the disease focus.